Bobbin, motor, and method of winding magnet wire

Abstract

A bobbin comprises three hollow-cylindrical sections, specifically a middle body section, and two lateral body sections. The middle body section has its diameter diminished compared to the two lateral body sections thus forming an annular recess which allows a magnet wire to be wound with an additional number of turns around the bobbin without increasing a motor size. With this bobbin structure, when the number of turns of a magnet wire is set to remain unchanged, the diameter of flanges of the bobbin can be reduced resulting in a downsized motor.

1. A stepping motor comprising:
 a rotor assembly shaped cylindrical, having a rotary shaft fixedly attached to its center, and having a plurality of magnetic poles arranged at its outer circumference; 
 a first yoke formed of a soft-magnetic plate, having an opening for rotatably letting the rotor assembly through, and having a plurality of pole teeth formed at a circumference thereof defined by the opening so as to oppose the plurality of magnetic poles with a predetermined clearance in-between; 
 a second yoke formed of a soft-magnetic plate, disposed to oppose the first yoke, having an opening for rotatably letting the rotor assembly through, and having a plurality of pole teeth formed at a circumference thereof defined by the opening so as to oppose the plurality of magnetic poles with a predetermined clearance in-between; 
 a magnetic path means to magnetically connect the first and second yokes; and a bobbin including 
 a middle body section shaped hollow-cylindrical, 
 a first lateral body section shaped hollow-cylindrical and having a larger bore diameter and a larger outside diameter than the middle body section, 
 a second lateral body section shaped hollow-cylindrical and having a larger bore diameter and a larger outside diameter than the middle body section, 
 a first joining section to connect one end of the first lateral body section to one end of the middle body section in a coaxial manner, 
 a second joining section to connect one end of the second lateral body section to the other end of the middle body section in a coaxial manner, 
 a first flange formed at the other end of the first lateral body section so as to radially extend outward, and 
 a second flange formed at the other end of the second lateral body section so as to radially extend outward, 
 the bobbin having a magnet wire wound around the first lateral body section, the middle body section, and the second lateral body section, the bobbin having a distance between an outer face of the first flange and the first joining section larger than the length of the plurality of pole teeth of the first yoke and a distance between an outer face of the second flange and the second joining section larger than the length of the plurality of pole teeth of the second yoke such that the plurality of pole teeth of the first and second yokes are housed inside of the first and second lateral body section respectively. 
 
   
   
     2. A stepping motor according to  claim 1 , wherein a plurality of stator units are provided, each of the stator units including the first and second yokes, and the bobbin. 
   
   
     3. A stepping motor according to  claim 1 , wherein the first joining section is shaped like an annular ring oriented perpendicular to a longitudinal direction of the middle body section and the first lateral body section so as to form a step configuration, and wherein the second joining section is shaped like an annular ring oriented perpendicular to the longitudinal direction of the middle body section and the second lateral body section so as to form a step configuration. 
   
   
     4. A stepping motor according to  claim 1 , wherein the first joining section is sloped with respect to outer surfaces of the middle body section and the first lateral body section, and wherein the second joining section is sloped with respect to outer surfaces of the middle body section and the second lateral body section.